1. Field of the Invention
This invention pertains to the art of producing decorative designs on glass and similar substrates by means of a sand blasting technique. The invention is more particularly directed toward a method of sandblasting intricate designs on glass or the like and an article of manufacture which is useful for carrying out the method.
2. Description of Related Art
A useful method of providing permanent decorative designs on various types of glass articles such as windows, drinking glasses, mirrors, etc., usually involves sandblasting designated portions of the glass surface to erode those portions while leaving the remaining portions untouched by the sandblast. The sandblasting erodes the glass to produce a cut-away area which has a "frosted" appearance. The frosted appearance of the eroded portion provides an effective contrast for the untouched smooth transparent portion of the glass. By carefully controlling the areas which are sandblasted, a contrasting array of eroded and smooth areas can be produced on the glass in the form of a picture, artistic design, lettering, etc.
In order to produce adequate contrast, it is important to provide a sharp cut-off between the eroded areas and the smooth non-eroded areas. By providing a sharp cut-off, the design will have good definition. In the past, various types of stencils have been proposed for this purpose. Typically, these stencils shield or mask the areas which are to be left smooth and allow the sandblast to erode the unshielded areas.
One type of stencil is disclosed in U.S. Pat. No. 174,167. The stencil described in this patent comprises a sheet of pulverizable paper with an ink resist design adhered to one side thereof. In order to apply the stencil to the glass, it is first necessary to apply a layer of liquid paste onto the glass surface in a separate manual operator step before applying the stencil to the glass. The stencil itself lacks adhesive. The paste is a solution of dextrin in an aqueous solution containing a little ammonia. This separate step of applying the paste solution to the glass is difficult for an operator to accomplish in an acceptable manner because the thickness of the paste on the glass must be uniform and very thin so that it does not interfere with the sandblasting. It has not been possible with this method to apply sufficient paste to assure adhesion while at the same time not interfering with the sandblasting process. In addition, the operation of applying liquid paste to the glass is a messy operation and very time consuming.
U.S. Pat. No. 1,594,603 discloses a method of sandblasting an ornamental design on stone or similar substrates. The method uses a sheet of soft packing material, such as blotting paper, which is held in place on the stone directly underneath a stencil. The stencil and packing material are utilized as separate elements which is inconvenient and requires additional operator steps to individually place and secure the stencil and the packing material onto the stone surface. Furthermore, the method of securing these materials to the stone involves the use of clamps and there is no suggestion to use paste to secure the stencil and packing material onto the stone. The prior art use of paste is not suggested and, thus, appears to be abandoned in favor of the clamps for securing the stencil and packing material to the stone. While the use of clamps and the like will avoid the inherent problems with respect to the application of liquid paste onto the glass, it creates other difficulties which makes the method described in U.S. Pat. No. 1,594,603 especially undesirable for producing designs on glass. For example, the clamps are clumsy and expensive and their use also requires additional operator steps which makes the overall process inefficient.
Finally, in U.S. Pat. No. 3,267,621, a process is described for sandblasting a decorative design on a glass article. In this process the problems associated with the prior art methods are said to be solved by directly applying a resist layer onto the glass in the form of a design by means of a silkscreening process. No paper substrate is used since the resist layer is silkscreened directly onto the glass. While this method may avoid some of the problems associated with pasting paper-backed stencils onto glass substrates and the problems associated with the use of clamps, this method creates additional problems which make the overall process unattractive for efficient production of decorated glass articles. For example, a liquid adhesive needs to be applied to the glass surface to assure adequate bonding of the resist layer to the glass. Thus, effective use of this process requires an additional adhesive application step to complete the process. In addition, one cannot utilize a separate design decal for later use or for easy shipping to another location for the sandblasting process because the design is silkscreened directly onto the glass. Also, both the silkscreening process and the sandblasting process require the handling of the glass. Each time the glass is handled, the probability of glass breakage increases.
Since the date that U.S. Pat. No. 174,167 issued, to the present time, no one has been able to provide a simple and effective method and article for enabling the sandblasting of precise and intricate designs on glass surfaces. The particular problems associated with the art since the issue of U.S. Pat. No. 174,167, over one hundred and ten years ago, demonstrates the longfelt need for improvements to overcome the above-mentioned problems. The failure of others to develop and make effective use of a self-adhesive, paper-backed stencil for sandblasting and the eventual abandonment of a paper backing in favor of direct silk-screening onto the glass substrate, illustrates that there is no obvious solution available to solve these problems of longfelt duration.
Therefore, there remains a need in the art for providing a convenient and easy to use self-adhesive stencil for sandblasting designs on glass surfaces and which avoids the heretofore mentioned problems associated with the prior art.